In a typical liquid crystal display (LCD) device, light emitting diodes (LEDs) are adopted as backlight sources. A specific principle is that a plurality of LEDs are connected in series to form an LED lightbar. For a large LCD device, a plurality of LED lightbars shall be connected in parallel for use. Each LED lightbar is connected in series with a dimming controllable switch for dimming. When the LED lightbars are short-circuited, or several LEDs in one LED lightbar are short-circuited, the dimming controllable switch will withstand a high voltage difference when being switched off and will be easily damaged.